Different fuels emit different amounts of carbon dioxide in relation to the energy they produce. To compare emissions across fuels you must compare the amount of CO₂ emitted per unit of energy output or heat content.

Pounds of CO₂ emitted per million Btu of energy for various fuels:

Coal (anthracite)	227
Coal (bituminous)	205
Coal (lignite)	215
Coal (subbituminous)	213
Diesel fuel & heating oil	161
Gasoline	156
Propane	139
Natural gas	117

The amount of CO₂ produced when a fuel is burned is a function of the carbon content of the fuel. The heat content or amount of energy produced when a fuel is burned is a function of primarily the carbon (C) and hydrogen (H) content of the fuel. Heat is produced when C and H combine with oxygen (O) during combustion. Because natural gas is primarily methane, or CH₄, it has a relatively high energy content relative to other fuels, and thus a relatively low CO₂ to energy content. Water and various elements such as sulfur and non-combustible elements in some fuels reduce their heating values and increase their CO₂ to heat contents.

Carbon dioxide emissions per physical unit and million Btu for numerous fuels

Last reviewed: January 15, 2010

There are various ways to compare carbon dioxide emissions across countries including: total carbon dioxide emissions, carbon dioxide emissions per capita, and carbon dioxide intensity. The data below are for energy-related carbon dioxide emissions as EIA does not have comparative data for carbon dioxide emissions from industrial processes for all countries.

• Energy-related carbon dioxide emissions — In 2008, the United States emitted 5,833 million metric tons of carbon dioxide from the consumption of fossil fuels.

Million metric tons of carbon dioxide emitted in 2008:

United States	5,833 (19% of world total)
China	6,534 (22% of the world total)
Europe	4,662 (15% of world total)
World Total	30,577

• Carbon dioxide emissions per capita — In 2008, the per capita carbon dioxide emissions in the United States were about 19 metric tons. Per capita carbon dioxide emissions in the United States have not varied much over time, because the rate of growth of carbon dioxide emissions has been about the same as the growth in population.

Metric tons of carbon dioxide emitted per capita in 2008:

• United States — 19.2
• China — 4.9
• Europe — 7.8
  
• World Average — 4.5

• Carbon dioxide intensity — A nation’s carbon dioxide intensity is typically expressed as metric tons carbon dioxide (MTCO₂) per unit of economic activity. In 2008, U.S. carbon dioxide intensity was 443 MTCO₂ per million dollars of Gross Domestic Product (GDP), based on the value of the U.S. dollar in 2005.

Carbon dioxide intensity in 2008 expressed as MTCO₂/$ million GDP (calculated using Purchasing Power Parity in 2005 dollars), for selected region and the world:

• United States — 443
• China — 880
• Europe — 298
• World Average — 464
  

The International Energy Statistics portal has historical emissions estimates for all countries.

International Energy Outlook 2010, Chapter 8 has tables with historical data and forecasts, for regions and selected countries and by fuel types.

Last reviewed: January 4, 2010

Greenhouse gas emissions by sector in 2008 for the United States (Million Metric Tons of Carbon Dioxide Equivalent)

¹ Methane, nitrous oxide, and high global warming potential gases.

Emissions of Greenhouse Gases in the United States, 2008 reports EIA’s latest annual emissions data.

Most recent data on carbon dioxide emissions.

Last updated: January 19, 2010

Total U.S. electricity-related emissions of greenhouse gases in 2008 were 2,499.8 million metric tons (MMT) of carbon dioxide equivalent (CO₂e), or about 35% of total U.S. greenhouse gas emissions.

Total electricity-related emissions include:

• 2,477.2 MMT of CO₂ emissions from conventional power and combined-heat-and-power plants, which was about 42% of total CO₂ emissions and 43% of energy-related CO₂ emissions, and includes:
• 2,359.1 MMT of CO₂ from the electric power sector, which includes power plants operated primarily for the generation and sale of electricity,
• 118.1 MMT of CO₂ from the industrial and commercial sectors, which includes industrial, commercial, and institutional facilities with generators (usually combined heat and power plants) primarily for the direct use of the electricity by the facilities
• 0.8 MMT CO₂e of methane (CH4), 0.1% of total CH4 emissions
• 9.7 MMT CO₂e of nitrous oxide (N₂O), 3.2% of total N₂O emissions¹
• 12.1 MMT CO₂e of sulfur hexafluoride from leaking electricity transmission equipment where sulfur hexafluoride is used for insulation.

Emissions of Greenhouse Gases in the United States contains EIA’s detailed annual estimates of emissions for all reported greenhouse gases.

Electric Power Annual contains historical data on CO₂ emissions from all electricity generation (conventional power plants and combined-heat-and-power plants).

Monthly Energy Review (Table 12.6) contains most recent estimates of CO₂ emissions by the electric power sector.

¹N₂O, a byproduct of fuel combustion, should not to be confused with nitrogen oxides, or NOx, which are also byproducts of fuel combustion that are regulated by the U.S. Environmental Protection Agency but are not direct greenhouse gases.

Last updated: January 22, 2010

EIA publishes emission factors (or coefficients) for three major greenhouse gases: Carbon Dioxide (CO₂), Methane (CH₄) and Nitrous Oxide (N₂0), and for the criteria air pollutants; Sulfur Dioxide (SO₂) and Nitrogen Oxides (NO_x), which are released when fuels are burned and when electricity is generated and used as follows:

For combustion of fossil fuels:

   CO₂ for common fuels, in pounds per physical unit and per million Btu.

   CO₂ for fuels used for electricity generation, in pounds per million Btu.

For electricity — as generated:

   CO₂, SO₂, and NO_x for electricity generated in each state for a specific year, in pounds per megawatthour, in Table 1 of State Electricity Profiles and averages for the United States.

   CO₂, CH₄, and N₂0 for electricity generated in each state and U.S. Census Region, in pounds per kilowatthour (weighted average for years 1998 to 2000).

For electricity — as consumed:

   CO₂ in metric tons per megawatthour, and CH₄ and N₂0 in kilograms per megawatthour, for electricity consumed in U.S. electricity market regions and in other countries (weighted average for years 1999 to 2002 and 1991 to 1994). These factors are used by participants in EIA’s Voluntary Reporting of Greenhouse Gas Emissions program.

A source of emission factors for other substances and fuels is the U.S. Environmental Protection Agency.

Last updated: January 29, 2010

Energy-related carbon dioxide emissions from fossil fuels, 2008 (Million Metric Tons)

¹Includes combustion and flaring of natural gas.

International statistics on energy-related carbon dioxide emissions.

Last updated: January 28, 2010

No. Water vapor is the most abundant greenhouse gas, but most scientists believe that human activity has a very small effect on its concentration in the atmosphere, and therefore EIA does not estimate emissions of water vapor. Recent research by NASA suggests a stronger role from the indirect human effects on water vapor concentrations.

What are greenhouse gases and how much are emitted by the United States?

Last reviewed: January 12, 2010